The present invention relates to a method and apparatus for testing webs of flexible material, especially webs of cigarette paper, imitation cork of other wrapping material for commodities which constitute or form part of smokers' products. More particularly, the invention relates to improvements in a method and apparatus for monitoring the locations of holes, pores or like openings (hereinafter called perforations) in webs of wrapping material for filter cigarettes or the like. Still more particularly, the invention relates to improvements in a method and an apparatus which can be resorted to with advantage for monitoring of the quality or condition of so-called tipping paper, i.e., wrapping material which is used in filter tipping machines to form uniting bands serving to connect plain cigarettes with filter rod sections of unit length or multiple unit length so as to convert such articles into filter cigarettes of unit length or multiple unit length.
It is well known to form tipping paper (e.g., cigarette paper or a similar flexible web- or strip-shaped material which often imitates cork) with perforations by resorting to a mechanical perforator (such as a set of needles), to a system of electrodes which generate sparks to burn holes in a web of tipping material passing through the gap or gaps between complementary electrodes, or to one or more lasers or other sources of coherent radiation. The art is replete with proposals to make perforations in such material, and the purpose of perforations is to allow a certain amount of cool atmospheric air to flow into the column of tobacco smoke, it being believed or hoped that that the atmospheric air will reduce the percentage of nicotine, condensate and/or other deleterious ingredients of tobacco smoke which reach the mouth and/or the lungs of the smoker. The perforations in tipping paper can be formed at the plant where such paper is produced and rolled to form bobbins or reels which are transported to the tobacco processing plants for use as uniting bands in filter tipping or analogous machines. It is also possible to form perforations in cigarette paper which is used to form wrappers around rod-like fillers of tobacco, i.e., to form plain cigarettes of desired length. As a rule the perforations are close to that end of a cigarette which is to be inserted into the mouth, and the combined cross-sectional area of such perforations must closely approximate or match an optimum value which is considered to produce best results as far as the reduction of danger of tobacco smoke to the health of the smoker is concerned.
In a filter tipping machine, the web of perforated tipping material is transported along a paster which coats selected portions of the web (such portions are not supposed to include the portions which are provided wth perforations) with a suitable adhesive before the web is subdivided into discrete uniting bands which are then draped around filter plugs and around the adjacent end portions of plain cigarettes. In many instances, the tipping paper has two rows or groups of rows of perforations each of which is adjacent to a different marginal portion of the web. This is necessary in filter tipping machines which are designed to make filter cigarettes of double unit length. Such cigarettes are thereupon severed midway between their ends so that each thereof yields two discrete filter cigarettes of unit length. The severing takes place midway between the axial ends of the convoluted uniting band, and each half of the band must be provided with a group of perforations, preferably close to the locus where the filter plug of unit length abuts against the adjacent end portion of the plain cigarette. Reference is made here to filter tipping machines of the type known as MAX and MAX S which are produced by the assignee of the present invention and are designed to make filter cigarettes of double unit length which are thereupon severed to yield pairs of filter cigarettes of unit length.
As mentioned above, it is considered important and desirable to ensure that the convoluted uniting band of each and every filter cigarette exhibit a predetermined permeablilty which matches or at least closely approximates a desirable optimum or presumably optimum value. This can be achieved by ensuring that the perforated zone or zones of tipping paper are not coated with adhesive because the adhesive (irrespective of whether a wet adhesive or a hotmelt) will clog at least some of the perforations so that the permeability of such tipping paper to air downstream of the paster is less than the permeability of tipping paper which has been coated with adhesive only in the regions that are remote from the perforated region or regions. Since the tipping paper is normally, or at least often, perforated in the manufacturing plant where the paper is made rather than in the cigarette making factory, the measures which the maker of cigarettes can undertake to avoid unsatisfactory coating with adhesive include proper guidance of the web of tipping paper during travel along the paster. However, this prevents the application of adhesive only if the position of perforations in the running web of tipping material is always the same, i.e., if the perforations are located at a prescribed or anticipated distance from the marginal portions of the web. In the absence of predictability in the positions of perforations with reference to the marginal portions of the web, the paster is likely to apply adhesive to perforated regions even if the web of tipping paper is guided with the utmost degree of accuracy.
It has been found that the locations of perforated zones in successive webs of tipping paper often deviate, quite pronouncedly, from optimum locations. This brings about the aforediscussed disadvantages as well as many others. Thus, not only is the paster likely to clog some or all of the perforations in the running web of tipping paper but the perforations can be too close to the lip ends of filter mouthpieces in filter cigarettes so that they are likely to be sealed by the lips of the smoker. Moreover, and if the perforations are of such size and/or shape that they can be seen with the naked eye, improperly applied and/or distributed perforations (or the adhesive paste penetrating through such perforations) will detract from the eye-pleasing appearance of the smokers' products. A manufacturer who relies on accuracy in the positions of perforations in the webs of tipping paper is likely to produce huge quantities of filter cigarettes with unsatisfactory ventilating (air-admitting) zones or to produce filter cigarettes which are totally devoid of ventilation zones. It must be borne in mind that a modern cigarette maker or filter tipping machine can turn out up to and in excess of 100 cigarettes per second, and that a single bobbin or reel of tipping paper with unsatisfactory perforations is likely to cause huge losses in output or the production of large quantities of unsatisfactory smokers' products. Spot checking of such products, even at relatively frequent intervals, does not appreciably reduce the number of rejects in view of the aforementioned extremely high output of modern cigarette makers and like machines. On the other hand, testing of each and every product for the presence of absence of satisfactory ventilation zones is a very complex and costly procedure, especially if such testing must be performed in addition to customary testing which involves detection of frayed ends of wrappers, large holes in the wrappers, open ends, absence of sufficiently dense ends and similar defects which are normally detected in heretofore known testing devices forming part of or cooperating with cigarette making, filter rod making or filter tipping machines. Furthermore, if a cigarette having an unsatisfactory ventilation zone is detected in or after it is removed from the maker, the machine is likely to have produced an enormous quantity of unsatisfactory rod-shaped articles before the cause of defect is detected and eliminated.